Transforming of acoustic swingings into electric capacity swingings



Nov. 25, 1930. A. v. PETERSEN 1,783,138

TRANSFORMING OF ACOUSTIC SWINGINGS INTO ELECTRIC CAPACITY SWINGINGS 7 lhye VPeieluen A 7 Tony;- rs

Patented Nov. 25, 1930 UNITED sTA'r-Es rATENr- OFFICE TRANSFORMIN'G OF ACOUSTIC SWINGINGS INTO ELECTRIC CAPACITY SWIlVGINGS Application filed October 2, 1928, Serial No. 309,826, and in Denmark October 5, 1927.

My invention relates to the transforming of acoustic swingings into electric capacity swingings. The object of my invention is to produce a method and an apparatus for having it carried out, by which method and apparatus the transforming is effected in a direct manner not involving any movement of mechanical parts.

Several types of electrostatic or condenser like microphones have already been proposed .for transforming sound waves-into capacity swingings. However, the known apparatus of this kind are based on the principle of the sound waves varying the mutual distances of the condenser layers or lamels, the air *compressions or depressions of the sound waves producing variations of the cross di mension of the dielectric on account of the movements of one or some of the said lamels.

. Owing to this movability of the lamels the known electrostatic microphones do not present any essential advantage as compared with ordinary microphones based on the principle of resistance swingings. Inboth cases unfortunate effects, due to over swingings, sluggishness and the like, will affect the acoustic purity.

According to my present invention the capacity swingings of the microphone, in lieu of being produced by variations of the dimensions of the dielectric, are'produ'ced in' a direct manner through variations of the dielectricity constant.

My invention is based on the physical fact of the varying of the dielectricity con, stant with the pressure, especially as far as gases and vapours-are concerned. According to the invention I apply the said principle in amanner allowingthe sound sWingings to act directly without mechanical intermediate means, according to the invention the acoustic compressions and depressions in the air, or in gases or vapours, take place directly between unmovable condenser lamels. Thus the value of the dielectricity constant prevailingatany moment, depends upon the soundswinging appearing at that moment. a

Hence a capacity swinging corresponding to the sound swingings, produced direct-- cross bar12, or the like.

ly without the interference of any mechanical intermediate means.

In order to have my invention fully understood I have diagrammatically represented it on the drawing.

Figs. 1 and 2 show an example of an electrostatic microphone according to the invention, in plan view and section respectively.

Figs. 3-6 show examples of amplifying and employing the capacity swingings produced in the present manner. p

- The microphone shown in Figs. 1 and 2, consists of a number of parallel bar like members 6 and 7 of a suitable electrically conducting or half conducting material, preferably more or less soundless and being either uniform or heterogeneous. As materials of this kind are well known they need not be further specified. In many cases lead or lead alloysmay be employed.

The members 6 and 7 are by means of screws 8'or the like alternately and suitably tightly fixed on a base 9 so as to form suitable intermediate air spaces 10. The members 6 are mutuallyconnected by a cross bar 11, or the like, and the members 7 by a Of course, the mutual electric and mechanical connections of the members may be obtained in many different manners, for instance through long bolts, electrically connected with the one set of members and in sulatingly passing through the other set. If desired intermediate spacing rings or other suitable spacing means mav be inserted between the members 4 The latter need -not be straight as shown on the drawing. If preferred they may be of any curved shape. They may for instance consist of rings or segments and be'built in columns or the like. I

Although I fix the members 6 and 7 in a manner so as to be free of swingings, I do not exclude means for any desired adjustingof the capacity by altering the spacing of thev members,-for instance by sliding or 1 turning. If desired the present condenser like microphone may be of the variable type in lieu of the constant capacitytype.

As alteration of,these and similar kinds fact above set forth.

The dielectric need not be atmospheric air. In many cases suitable gases or vapours for instance in the neighbourhood of the condensing point, may be constantly led through the intermediate -spaces from a suitable source.

Further there may be arranged a chamber for the said gases or vapours, in which chamber the microphone is placed, the said chamher being provided with a wall or walls of a non sound absorbing kind.

As means for making such arrangements are well known, they are not shown on the drawing. 1

According to Fig. 3 the microphone mem bers 6 and 7 are connected each with its pole of a current source 13. When the capacity of the microphone is brought to swing in the present manner on account of sound waves, the electric swingings in the primary circuit 14 containing the said current source and the microphone, are through 15, 16 transformed to a sender circuit 17. I

In the example shown in Fig. 4 the circuit 14 contains a great resistance 18, and is connected with an amplifying circuit 19 contaming an audion lamp 20, a capacity 21, and provided with a.- resistance 22. From the amplifying circuit 19 a sender or a loud speaker may be actuated through a further amplifier 30.

According to Fig. 5 the circuit 14 connected to the amplifying circuit 19, is connected to an aerial 23 and tuned to a definite frequency. A generator, e. g. the aerial 24,

for swingings of the same frequencies, coacts with the circuit 14. When the microphone is actuated by sound waves the swinging amplitudes of the circuit 14 will then be varied in accordance with the capacity swingings caused by the sound Waves. Consequently the swingings in the circuit 14 will be modulated in accordance with the sound.

In Fig. 6 I have shown another sender v besides the sending circuit 14. which latter is tuned by the present microphone 6, 7 serving as a condenser. The sa d second sender presents a swinging circuit 25, WhlCh through a variable condenser 26 may be tuned to a frequency deviating a certain number of eriods from the frequency of the sending c rcuit 14.

p f The sending circuits 14 and 25 influence a common receiver circuit 27, which latter is thus damped so as to present a tune curve of a flatness allowing the frequencies of both sending circuits to lie within its maximum part, and from which circuit 27 the frequency difference is imported through a detector lamp 28. A secondary receiving circuit 29 is, thus tuned relative to the said frequency difference so that the latter is lying somewhat to the one or the other side of the maximum of its tune curve.

encing the microphone 6, 7 is brought to act as corresponding current intensity modulations in the circuit 29. The modulations are through a suitable amplifier 30 brought to act 1 bars and adapted for the reception of sound waves, whereby said conductors respond electrically but non-mechanically to said sound waves.

2. A sound receiving and transmittin sys tem including a microphone adapte for transforming of sound waves into electrical waves comprising rigidly mounted electrical conductor bars positioned for the accommodation of dielectric means therebetween, dielectric vapors interposed between said bars and in a state in which the dielectrioity constant is highly variable upon pressure and adapted for the reception of sound waves, whereby said conductors respond electrically but non-mechanically to said sound waves.

In testimony whereof I hereunto afiix my signature.

* AAGE V. PETERSEN.

Consequently the tune frequency caused by acoustically influ 

